The prevalence and laboratory predictors of iron deficiency in children with sickle cell disease (HbSS or HbSC) are being studied. Iron studies are being checked immediately before and 3 weeks after a single intramuscular dose of iron dextran (approximately 2.5 mg/kg). Initial laboratory studies will be compared between subjects who do and do not respond to the iron to determine which tests are most helpful in predicting iron deficiency in this population.